nixos/firefox: dedupe identically nativeMessageHosts packages (#335253)

            old.extraPrefsFiles or [ ]

            ++ cfg.autoConfigFiles

            ++ [ (pkgs.writeText "firefox-autoconfig.js" cfg.autoConfig) ];

          nativeMessagingHosts = old.nativeMessagingHosts or [ ] ++ cfg.nativeMessagingHosts.packages;

          nativeMessagingHosts = lib.unique (

            old.nativeMessagingHosts or [ ] ++ cfg.nativeMessagingHosts.packages

          );

          cfg = (old.cfg or { }) // cfg.wrapperConfig;

        }))

      ];